This invention relates generally to window constructions, and in particular to a window assembly which has a pair of sashes mounted in a generally rectangular outer frame for relative horizontal movement and which is intended for installation in a rough opening of a building wall such as, typically, the so-called curtain wall. The invention is still more particularly directed to the improved construction of the outer frame for such dual sash window assembly including means for wind-tightly sealing or filling the gap between the sill of the outer frame and the meeting or lapping portions of the two sashes.
Dual sash window assemblies are often employed with curtain walling which has decorative uprights on the external surface extending along the meeting portions of the window sashes. In such cases the sashes must be installed into or removed from the outer frame only from inside the room. Perhaps the simplest way of meeting this requirement is to increase the depth of downwardly opening grooves in the header of the outer frame. However, this measure is objectionable in that it necessitates too much increase in the dimension a (see FIG. 2 of the accompanying drawings) of the header. A decrease in the dimension b (FIG. 2) of the sill of the outer frame is also undesirable because then the window would not be sufficiently impervious to driving rains.
It has also been proposed to increase the height of a pair of parallel spaced rails on the sill of the outer frame in order that the sashes may be manipulated into and out of the outer frame from inside the room by taking advantage of the deep spacing between the sill rails. According to this proposal, however, the usual windtight sealing means installed between the sill rails must be manually moved away from and back to its predetermined position when the sashes are installed into the outer frame.